Why valuating ecosystem services at multiple scales?

To acknowledge the value of natural capital, one of society’s important assets, a better understanding of the patterns and spatial scales at which ecosystem services operate is essential to developing ecosystem services valuation (ESV) to support landscape-level conservation and land management plans.

Table 1. The four different classes of ecosystem services defined by the Millennium Ecosystem Assessment (MA 2005)

Supporting: services necessary for the production of other ecosystem services (e.g. nutrient and water cycling, photosynthesis

Ecosystem services (ESs) are benefits that can be provided by human-modified and natural systems. The structure and function of such systems represent a stock of natural capital providing flows of goods (such as food, timber, forage, and non-traditional forest products) and services (such as soil formation and nutrient/carbon storage, erosion control, water filtration, pollution assimilation, and recreation) that are valued by society. These goods and services constitute a large share of our social and economic welfare, and are vital to the Earth’s life-support system (Table 1). Biodiversity is a critical part in providing ecosystem services in that most are due to the component populations, species, functional groups (guilds), food webs, habitat types or mosaics of habitats and land uses that collectively produce them, i.e., the ecosystem service providers (the ESPs).

One of the greatest challenges facing humanity involves the understanding of distinct scales of environmental change and human response, and how the interplay of those scales has evolved historically, which is of paramount importance to get a better insight into how specific geographic areas are interrelated. A clear understanding of scale can lead to development of more effective environmental policies and management. It can tell the local land owners and jurisdictions whether or not they can protect and enhance ESs locally (through their actions alone) or whether they must rely on regional, national, or global environmental policies to achieve and sustain certain levels of ESs. For example, reduction of hypoxic or anoxic conditions in estuaries and near-shore marine environments requires reduction of nutrient inputs coming off of entire river basins. As such, a comprehensive understanding of scale relations across entire river basins is needed to improve and maintain estuarine and near-shore habitats.

Human activities have become so extensive that they have increased the interconnectivity of our global social-ecological system. This increased interconnectivity has resulted in a global scale alteration of some of our most important ESs. Resulting changes in ESs are caused by multiple interacting direct drivers such as land cover change, global changes in atmosphere and climate from industrial emissions, water use and availability due to irrigation, alien invasive species expansion, and local changes in species populations due to harvesting, habitat destruction and landscape degradation. Direct drivers operate at multiple scales and, in turn are controlled by indirect drivers (e.g., economic, demographic, or cultural changes) operating more diffusely, by altering one or more direct drivers. An example of how climate variabilty/change is magnified by impervious surface created through local or county level land use change (e.g., transition to urban and developed from agricultural lands) is given by Jennings and Jarnagin. Land-cover change has been identified as one of the most important drivers of change in ecosystems and their associated services, representing a primary human effect on natural systems and underlying fragmentation and habitat loss, which are the greatest threats to biodiversity.

At the landscape scale, the dynamic spatial con?guration resulting from human appropriation and management of regional landscapes can have a variety of ecological effects over a wide range of spatial scales. A direct effect is the alteration of ecological processes at local scales through the modi?cation of land cover. For example, converting forest to agriculture land cover alters soil biophysical and chemical properties and associated animal and microbial communities, and agricultural practices such as crop rotation alter the frequency of these disturbances. The spatial con?gurations of land cover in a region also affect ecological patterns and processes. This is one of the fundamental underlying concepts coming out of the field of landscape ecology that is spatial distribution and pattern affect important ecological flows (e.g., nutrients/materials, biota, energy, water) that sustain certain levels of ESs and their associated benefits. New land cover types can be juxtaposed and shifted within increasingly fragmented remnant native land cover types, and changes in the structure of the landscape can alter (in a negative way) nutrient transport and transformation, species persistence and biodiversity, and nurture invasive species.

Table 2. Ecosystem services, classified according to the Millennium Ecosystem Assessment (MEA 2005), and their direct and intermediate ecosystem service providers. Functional units refer to the unit of study for assessing functional contributions of ecosystem service providers; spatial scale indicates the scale(s) of operation of the service (Petrosillo et al. 2010; modified from Kremen, 2005)

Based on the last decade of research, we are beginning to understand the complex ways in which humans have affected and have been affected by natural systems of the Earth. Much work has been oriented to describe and categorize ESs, identify methods for economic valuation, mapping the supply and demand for services, assessing threats, and estimating economic values.

There is a growing demand for answers to questions like: How much of a watershed’s (catchment) area must be forest and where are the most important areas to maintain or restore in order to provide clean water for downstream communities? How should patches of different land uses/land covers be distributed within a rural landscape to provide flood regulation or pollination and pest control services for crops? Up to what distances might adjacent land uses affect the capacity of natural habitat to provide pest control and pollination services? Answers to these questions will help determine how different land uses and set-asides (protected designations) should be spatially distributed in the landscape in order to protect and manage ESs.

Ecosystem services valuation (ESV) is the process of assessing the contributions of ESs to certain sustainable scales, fair distribution, and efficient allocation of space and resources, like having an appropriate mix of land-use types across scales such that ESs can be maintained. There is also the need to move from general estimates to more specific statements at regional and local scales. To effectively manage changes in the flow of goods and service we need to incorporate ESV into resource management decisions. However, moving from general statements about the tremendous benefits nature provides to people to credible, quantitative estimates of ESs has proven difficult.

Among the crucial issues for obtaining reliable, quantitative estimates of ESs are those related to scales and interaction between services. Goods and services that humans obtain from ecosystems may span different scales in space and time, and can interact with one another in complex, often unpredictable ways. Improvements in the understanding of the patterns at multiple spatial and temporal scales at which ecosystem services operate are likely to provide more realistic ES values and also to improve ecosystem-based management practices.

Scales of operation of the services

Most ESs are broadly classified as operating on local, regional, global or multiple scales, and different providers of the same ES may operate across a range of spatial and temporal scales. Services can be localized, e.g., fruit from a single tree, or derived from a relatively large area, e.g., flood control by wetlands or climate regulation through carbon sequestration. ES providers are landscape- or habitat-wide or ecological community attributes, and can often be characterized by the component populations, species, functional groups (guilds), food webs or habitat types that collectively produce the services (Table 2). They can operate at different scales. So, for example, pollinators or native predators providing pest control on crops generally operate at a local scale, whereas forests contribute to climate regulation at local (shading), regional (rainfall patterns and albedo) and global (carbon sequestration) scales.

Costanza (2008) has recently classified the spatial characteristics of 17 ESs based not only on the scale of operation of the service, but also on the spatial proximity of service delivery to human bene?ciaries (Table 3). Services like carbon sequestration, which is an intermediate input to climate regulation, is classi?ed as global non-proximal. This is because the atmosphere is generally well-mixed and removing carbon dioxide (or other greenhouse gases) at any location is equivalent to removing it anywhere else. However, at local or even regional scale, in certain areas and during certain periods of the year, conditions of stratified thermal inversion may occur in the lower atmospheric layers resulting in respiratory distress and infections in people.

Local proximal services, on the other hand, are dependent on the spatial proximity of the ecosystem to the human bene?ciaries. Use values will be determined by local patterns of land use, human population settlements and proximity to beneficiaries. The recreational function of a landscape or ecosystem, for example, is not only de?ned by the land cover of a speci?c location (e.g. natural area) but depends also on accessibility properties (e.g. distance to roads) and the characteristics of the surrounding landscape. Also pollination requires that the ecosystem with pollinators be proximal to the land being pollinated.

Directional ?ow-related services are dependent on the ?ow from upstream to down-stream as is the case for water supply and water regulation. This kind of service is the basis for ecosystem service payments established in 1996 in Costa Rica to induce landowners to provide ecosystem services. In this case, downstream users pay upstream landowners to maintain forest cover on their land to benefit from protection of upstream ecosystem services. Other examples of this kind of service can be found where, like in Italy, the economic value of non-marketed services provided by forests for watershed protection and slope stability against landslides, can be very high.

The effects of land-use intensity on local biodiversity and ecological functioning depend on spatial scales much larger than a single field or land use/land cover. This demands a landscape perspective, which takes into account the spatial arrangement of surrounding land-use types at multiple scales. To be characterized adequately, pattern–process relationships must be assessed at the multiple scales relevant to the inherent structure (or rate) of the system (or process) being studied, or the scale of perception of the organism(s) providing the service (ESPs). In this respect, spatially explicit estimates of ES efficiency across landscapes at multiple scales that might inform land-use and management decisions are still lacking (Table 4).

The valuation process of ecosystem services (ESV) to more accurately represent their value needs to incorporate the non-linear properties of these services over space and time. In many field settings, like rural landscapes, there is a nested set of cycles, each occurring over its own range of scales. Some cycles occur annually, some take around a decade, and still others may take a century. Photosynthetic activity, for example, is a fundamental process necessary for the production of other ecosystem services like carbon fixation, oxygen and primary production. Photosynthetic activity can be highly variable over time and space, but it is often assumed to change linearly, i.e. at a steady, unvarying rate for each habitat considered. When it is measured by green index (NDVI) from satellite data it shows rather distinct and characteristic seasonal inter-annual periodicities for different broad land-use/land-cover categories corroborating well-known vegetation changes given by seasonal variations in climate and water regime as well agricultural practices. For example, in Apulia (south Italy) mean NDVI paths of land-use/land-cover show the greatest separation during the hot and dry summers owing to drought of semi-arid grasslands, and water regulation of forests.

Another example is coastal protection provided by wave attenuation by some sea grasses that may be at its maximum during summer, when plants are reproducing, at medium levels in spring and fall, and non-existent during winter, when density and biomass are low. Yet, in the Mediterranean, sandy beach erosion can be still mitigated during winter by the stranding of seagrass leaves. Non-linearity may occur also because of the interaction between services.

Synergism and trade-off among services

ESs may interact with one another in complex and unpredictable ways, and knowledge of the interactions among ESs is necessary for making sound decisions about how society manages the services. As to directional ?ow-related services, impounding streams for hydroelectric power, for example, may have negative consequences on downstream food provisioning by ?sheries. In other words, a synergism occurs when ESs interact with one another in a multiplicative or exponential way. Synergistic interactions can have positive and negative effects, and pose a major challenge to the management of ESs because the strength and direction of such interactions remains virtually unknown.

Trade-offs, in contrast, occur when the provision of one ES is reduced as a consequence of increased use of another ES. Agricultural production shows an inverse relationship with water quality and quantity, as we increase agricultural production, the quality of water and the quantity available tend to decrease. Thus, use of nutrients and pesticides to increase agricultural production can lead to critical declines in water quality that can often propagate down-stream. Trade-offs seem inevitable in many circumstances and will be critical for determining the outcome of environmental decisions. In some cases, a trade-off may be the consequence of an explicit choice; but in others, trade-offs arise without premeditation or awareness that they are taking place.

Ecosystem services in social-ecological systems

Table 4: Some examples of ecosystem service efficiency, which is a measure of effectiveness at performing the service, for different ecosystem services from the literature; services are classified as regulating or supporting according to the Millennium Ecosystem Assessment (MEA 2003) (modified from Kremen 2005).

Service classification

Service

Ecosystem service provider

Efficiency measure(s)

Examples (reference)

Regulating

Carbon storage

Tree species (per capita)

Biomass accumulation rate

Balvanera et al. (2005)

Regulating

Crop pollination

Bee species (per capita) or community

Pollen deposition per visit; seed or fruit set with and without bees

Kremen et al. (2002)

Regulating

Crop pollination

Bee species (per capita)

Ratio of pollen deposition to removal

Thomson and Goodell (2001)

Regulating

Disease control

Vertebrate host species (per capita)

Disease dilution rate

Ostfeld and LoGiudice (2003)

Regulating

Leaf litter decomposition in streams

Stream invertebrate species (per capita)

Leaf-shedding process rate

Jonsson et al. (2002)

Regulating

Pest control

Insect parasitoid species (per capita)

Parasitism rate

Kruess and Tscharntke (1994)

Regulating

Dung burial

Dung beetle species (per capita)

Burial rate

Larsen et al. (2005)

Regulating

Water flow regulation

Forest habitats

Water flow rate

Guo et al. (2000)

Regulating

Invasion resistance

Herbaceous community (native plus naturalized species)

Invader biomass m-2; change in resident biomass/unit invader

Zavaleta and Hulvey (2004)

Regulating

Soil stability on mountain slopes

Herbaceous species

Species diversity

Pohl et al. (2009)

Regulating

Disturbance regulation (as LULC change over time)

Perennial cultivations (olive groves and vineyards)

Pattern (composition and configuration) at multiple scales

Zurlini et al. (2007); Zaccarelli et al. (2008)

Regulating

Coastal protection, wave attenuation, habitat refugia, nursery

Mangrove forests, seagrass beds, and coral reefs

Density of plants, sedentary of animal material, and bathymetry

Koch et al. (2009)

Supporting

Bioturbation

Benthic marine invertebrate species (per capita)

Bioturbation potential index

Solan et al. (2004)

Supporting

Nutrient cycling, mineralization

Soil microbial community/functional groups

Process rates

Balser et al. (2001)

Supporting

Above-ground net primary productivity

Herbaceous community

Biomass accumulation rate

Reviewed in Schmid et al. (2001)

Supporting

Mineralization and decomposition

Herbaceous community

N leaching or retention; decomposition rate; microbial biomass, etc.

Reviewed in Schmid et al. (2001)

Supporting

Monthly LULC photosynthetic activity

Different land uses and land covers

Normalized Difference Vegetation Index (NDVI) from remote sensing

Zaccarelli et al. (2008)

Humans may interact with ecosystems at various scales as individuals or as representatives of organizations responding to environmental changes (e.g., climate, drought, desertification) through multiple pathways. Their responses may in turn alter feedbacks between climate, ecological and social systems, producing a complex web of multidirectional connections in time and space. Highly interlinked and connected systems transfer shocks through the system faster and more completely than systems that are more modular and disconnected. The most important consequence for our globally interconnected social-ecological system is that the dynamics of our economic system(s) are no longer determined by economics alone, but by the dynamics of the total environmental (economic and ecological) system.

Anthropogenic disturbances such as changes in land use are determined by the social component of social-ecological landscapes. Such component is made by groups of people, organized in a hierarchy at different levels (e.g., household, village, county, province, region, and nation), that result in a distinct set of spatial patterns and scales influencing fundamental ecological processes (e.g., flows of materials/nutrients, water, biota, and energy). These patterns and resulting processes formed by humans in turn affect the quality and amount of ESs that a particular socio-ecological landscape can provide. Any given land use system in the hierarchy is likely to overlap multiple ownership and jurisdictional boundaries. Within this “panarchy”, the participants can have differing views as to which set of ESs is desirable at each level of the panarchy. For example, scale determines different values of wetland services in the Netherlands for stakeholders at different jurisdictional levels. In this example, at the municipal scale, interests refer to recreation, reed cutting and fisheries, whereas at the provincial scale, main concerns are recreation, but also nature conservation. At the national level, nature conservation is by far the most important service.

Because of historical land-use legacies, decision hierarchies of social systems can often be intertwined with the natural hierarchies, scales and frequencies that may emerge at the ecosystem or landscape level. As humans act as a keystone species, the characteristic scales of particular phenomena like anthropogenic changes are deemed to entrain and constrain ecological processes that produce services, and to be related to the scales of human interactions with the biophysical environment. If the patterns or scales of human land use change, then the structure and dynamics of the system as a whole can change accordingly, leading to transitions between alternative phases, when the integral structure of the systems is changed. In other words, people can structure landscapes leading to a set of different ecological flows that result in different levels (and types) of ESs. Alternatively, natural biophysical conditions can structure what humans do on the landscape, for example, in mountainous regions where agriculture occurs in the river bottoms or valleys but not on the mountains.

The emergence of new scales in the panarchy also adds to the complexity. The formation and expansion of the European Union and the World Trade Organization globally, or catchment management authorities and land-care groups locally can be examples of relatively new institutions. All of these institutions create new scales of management and interaction among services that in?uence and are in?uenced by the scales above and below them, ultimately in?uencing how ecosystem services are managed on the ground. Moreover, the degree to which this can be done depends also on whether the biophysical setting constrains how humans develop and use the landscape. In Italy, for example, there are not too many natural constraints but rather constrains of social and economic nature. But in other places like Switzerland, there are significant biophysical constraints on what gets developed due to mountainous landscapes.

Cross scale effects

Local processes are often spread and become important only when they merge at regional (for example, large agricultural land aggregations) or global scales (for example, carbon emissions that change the global atmosphere), but ecosystem services at more aggregated scales are seldom simple summations of the services at finer scales. Conversely, most services are delivered at the local scale, but their supply is influenced by regional or global-scale processes. Often local communities obtain some ecosystem services from other geographies. This is the origin of cross scale effects.

The increasingly connected and dynamic nature of social-ecological systems means that cross scale interactions are becoming more common. As these connections increase and strengthen, cross scale effects penetrate further across the scale hierarchy. Gunderson and Holling (2002) describe the way in which these linked scales in?uence each other, drawing on numerous examples from ecological and social systems to articulate the in?uence of cross scale effects. But it is in linked social–ecological systems where cross scale effects become so critical that spatial mismatches are expected when the spatial scales of management and the spatial scales of ecosystem processes do not align properly leading to disruptions of social-ecological systems, inefficiencies, and/or loss of important ecological components. Habitats, for instance, are often managed at a local level and hence are disassociated with other efforts in a region. Yet, to maintain biological diversity, especially for animals like migratory birds, one needs to have a management system that sets regional priorities. These regional priorities must then constrain what is done at the local scale. Mismatches often occur as this almost never happens.

Although there are many case studies, our capability of predicting emergence of cross-scale effects and their impacts on ESs is limited. Currently, the fundamental cross-scale challenge is the mismatch between the dynamics of natural systems and the dynamics of human management systems. Social and ecological scales might be, but are not always, aligned. This can lead to failures in feedback, when, for instance, benefits occur at one scale, but costs are carried at another.

A better understanding of the historical evolution of the web of connections and how to adapt to future surprises will lead to the most appropriate future responses and feedbacks within social-ecological systems. To develop that understanding, we need robust, manageable frameworks for analyzing ecosystem services at multiple time and space scales. Multi-scale assessment at any scale will be improved by information and perspectives from other scales.

Limits of reductionist approaches

Theories and approaches to ecosystems and landscapes have to a large extent focused on single issues or resources and been based on single scale or a few different distinct scales with a steady-state view, interpreting change as gradual and incremental, in most cases disregarding patterns across a continuum of scales and interactions across scales with social-economic components.

Also addressing the social and economical dimensions of landscapes without an understanding of resource and ecosystem dynamics will not be sufficient to lead society to sustainable outcomes. In interlinked social-ecological systems it may be easiest to analyze social and ecological attributes and functions separately.

However, such an approach may be at the expense of changes in the capacity of ecosystems to sustain the adaptation and it could affect the quality of ecosystem goods and services. This is because it could degrade natural renewable and non-renewable resources and generate traps and breakpoints in the whole system eventually leads to a transition to a new phase that results in degraded levels of ESs.

Such partial approaches are less likely to be useful under global environmental change wherein the capacity of many ecosystems to generate ESs for human welfare has become vulnerable and no longer can be taken for granted.

Current approaches to ecosystem service valuation

There are two main approaches for the generation of ES valuation (ESV) that aim to influence policy decisions.

According to the first approach, researchers use broad-scale assessments of multiple services to extrapolate a few estimates of values, usually derived from the coefficients based on habitat types to entire regions or the entire planet. Although straightforward, this approach assumes that every hectare of a given habitat type is of equal value – regardless of its quality, rarity, spatial configuration, size, proximity to beneficiaries, or the prevailing social practices and values. This approach assumes that ESs are changing linearly, i.e. at an unvarying rate for each habitat considered, and does not allow for analyses of service provision and changes in value under new conditions. For example, if a forest is converted to agricultural land, how will this affect the provision of clean drinking water, downstream flooding and fish diversity, and soil fertility? Without information on the consequences of land-use management practices on ES production, it is hard to design policies or payment programs to foster the desired ESs.

In contrast, according to the second approach for generating policy-relevant ES assessments, researchers carefully model the production of a single service in a small area through “ecological production function” to relate the provision of that service to local ecological variables. However, studies of biodiversity–function often examine communities whose structures differ markedly from those providing services in real landscapes, and have been restricted to a small set of ecosystem processes.

While each of those approaches have provided many valuable insights, a bridge is needed between these two approaches, i.e., one that will provide fundamental, ecological understanding of ecosystem services to assist in realizing the best management and policy tools for their conservation and sustainable use. What is needed are new approaches joining the rigor of the small-scale studies with the extent of broad-scale assessments adopting a landscape perspective.

Perspectives in ecosystem service valuation

Can we manage our social–ecological systems at the local, regional, national or even the global scale to be able to cope with shocks or in?uences that may come from any one of the multitude of scales that we are now inextricably linked through our increasingly interconnected society? In this direction, here are few points to address:

We have to look at social-ecological system dynamics in the context of complex adaptive socioeconomic and ecological systems, integrating phenomena across multiple scales of space, time and organizational complexity. The fundamental cross-scale challenge is the mismatch between the dynamics of natural systems and the dynamics of human management. Social and ecological scales might be, but not always, aligned. This can lead to failures in feedback, when, for instance, benefits ensue at one scale, but costs are carried at another.

We need rendering tool that displays the vulnerability across multiple scales of key sectors like agriculture, forestry, carbon storage and energy, water and biodiversity in order to address scale issues which are of importance in terms of environmental security, to inform public policy at a variety of organizational levels. Stakeholder input is useful to help quantify local and regional adaptive capacity, while climate and land-use models can be used to estimate potential impacts. Adaptive capacity and potential impacts together define the overall vulnerability of individual ESs.

A better understanding of landscape legacies is needed, and of the significance and value of the outputs of ESs and biodiversity together with potential scale mismatches between management and ecological processes generating ESs. In this respect, we need a better understanding of the historical evolution of this web of connections to ensure appropriate future responses and feedbacks within the human-environment system and how to adapt to future surprises. ES valuation needs to include natural variability in calculations of ESs provided when, for example, restoring coastal biotic structures for the purpose of improving coastal protection.

The effects of land-use intensity on local biodiversity and ecological functioning depend on spatial scales much larger than a single field or land use/land cover, and therefore it is important to link spatial patterns and ecological processes at a landscape scale. This demands a landscape perspective, which takes into account the spatial arrangement of surrounding land-use types at multiple scales.

In order to maintain services, the maintenance of the component habitat types or mosaics of habitats and land uses that collectively produce them rather than management for individual taxa may be a more effective way of using limited resources to benefit the greatest number of ES provider species (coarse filter approach).To effectively manage changes in the flow of goods and services, we must identify policy levers that affect human behavior (such as zoning regulations, taxes, incentives, services, and other infrastructure support) so that decision-makers can understand their effects on the provisioning of ecosystem goods and services.

Integrated modeling tools can allow predictions of the effects on biodiversity on ESs from changes associated with land uses at multiple scales and organizational levels, correlating changes in human well-being with past, present, and future changes in climate and land-use. In this respect, there is a strong need of the development of scenarios that can be used in full, or in part, in established planning processes to inform the land management and policy decisions, including for adaptation to and mitigation of climate change. Critical to progress in this area will be the development of spatially explicit landscape models that consider horizontal as well as vertical flows in fundamental ecological processes related to energy, materials/nutrients, water, and biotic fluxes and flows, and how the spatial pattern and intensity of land use affect these flows.